Minneapolis police issued a warning Wednesday after several bikers were robbed -- some at knifepoint and one with a gun -- on the popular Midtown Greenway and a connecting route.

The safety of greenway users has been a concern since before it was even built because the middle third of the 5 1/2-mile route paralleling Lake Street lies in a former railroad trench. So extra features such as 911 call kiosks, security cameras and extra lighting were installed.

But that hasn't prevented about 10 attacks in recent weeks aimed at bikers on the trails. Typically, police said, they involve several men who block the trails and take backpacks, wallets, electronics and purses, but not bikes.

The robberies prompted police to step up patrols and some riders to ride without lights to avoid detection by assailants. A grassroots, Web-connected group has organized a Saturday afternoon ride called "Take Back the Greenway."

Erez Biglajzer was knocked off his bike at around 10 p.m. on Nov. 20 by a man who rushed onto the trail on a curve, joined by two accomplices. He said he was kicked several times in the ribs and threatened with a knife. The attack, near where Cedar Avenue crosses the greenway, ended as another rider neared. Attackers wrestled away his iPod but not his backpack.

Now, unless he's riding with a friend, he avoids the greenway at night. But he still commutes on it during the day and will return at night if police patrols leave him feeling safer.

IF YOU GO

A "Take Back the Greenway" ride on Saturday has been organized by concerned cyclists. They plan to gather at 4 p.m. at the Dean Parkway green- way access ramp.

"I just could- n't believe it. I didn't expect it," he said of the attack. "I probably should have avoided the greenway at night but it's just so convenient."

Police think there may be more attacks that haven't been reported, and there also have been close calls.

"We also know of near-misses where the cyclists were going very fast and the assailants moved out of the way for their own safety," said Tim Springer, staff director for the Midtown Green Coalition advocacy group.

Police are advising bikers to avoid the greenway after dark, if that's possible, or to ride with others. "There's still a lot of people biking that bike trail after dark and they're not getting robbed," said police crime prevention specialist Don Greeley.

Paul Ashman, a frequent greenway user, said Wednesday that he plans to keep using it despite the recent attacks and an attempted robbery aimed at a friend one night earlier this year on a connecting trail.

"I hate that, I love the greenway and I want it to be safe," he said.

Police also want to hear from bikers who haven't reported incidents on the greenway or the connecting Hiawatha LRT Trail, which has less lighting. The greenway coalition has logged at least four attacks on the Hiawatha trail.

In one case, which Springer called "particularly disturbing," bike commuter Troy Melhus, a Star Tribune employee, was ordered off his bike last week by three men who blocked his path on the Hiwatha trail just south of the Franklin Avenue light-rail stop. A gun was held to the back of his neck and a backpack containing clothes and electronic gear was taken.

The greenway runs through two police precincts, both of which have security cameras trained on portions of the route.

Fifth Precinct Lt. Dave Hayhoe said it appears that more than one group of attackers is operating. He counted about a half-dozen incidents in which bikers have been robbed on the greenway or its ramps in the past two months.; Springer said the coalition has gotten reports of several others on the Hiawatha LRT Trail, which connects the greenway and downtown.

Since the recent snow, no robberies have been reported, Hayhoe said. But police presence will be increased in the area. Police are talking with the coalition about a citizens patrol starting next spring.